1. Field of the Invention
The present invention relates to a method for automatically lapping a work piece and a lapping apparatus using the same. More particularly, it relates to a lapping method for continuously lapping the work piece and a lapping apparatus using the same.
For example, after forming a magnetic head thin film, the magnetic head thin film is lapped on the process of manufacturing a magnetic head. Heights of a magnetic resistance layer and a gap of the magnetic head thin film of the magnetic head are made to have a certain constant by lapping on the manufacturing process of the magnetic head.
For the heights of the magnetic resistance layer and the gap, sub-micron order of accuracy is required. Therefore, it is necessary to lap work pieces or magnetic thin films with high accuracy.
2. Description of the Related Art
FIGS. 21A and 21B are explanatory diagrams of a composite type magnetic head.
As shown in FIG. 21A, the composite type magnetic head includes a magnetic resistance element 82 formed on a base plate 81 and a writing element 85. The magnetic resistance element 82 is formed of a magnetic resistance film 83 and a pair of conducting films 84 as shown in FIG. 21B. A resistance value of the magnetic resistance element 82 is varied by an external magnetic field. The magnetic resistance element 82 has a function to read out an electric current having a value according to magnetic field strength of a track 90 on a magnetic disk.
As the magnetic resistance element 82 is an element for reading out the current, it is required to provide a different element 85 for writing. The writing element 85 includes an inductive head. The inductive head is comprised of a lower magnetic pole 86, an upper magnetic pole 88 faced to the lower magnetic pole 86 with a certain gap, and a coil 87 provided between the lower and upper magnetic poles 86 and 88 to magnetically excite them. A non-magnetic insulating layer 89 is provided around the coil 87.
In such the composite type magnetic head, it is required to have a constant resistance value of the magnetic resistance film 83 in the magnetic resistance element 82 for each magnetic head. However, it is difficult to make the resistance value be constant or uniform on the process of manufacturing the thin film for the magnetic head. Therefore, after forming the thin film of the magnetic head, a height (width) h of the magnetic resistance film 83 is adjusted so that a resistance value may be uniformed.
FIGS. 22A, 22B, 23A, 23B, 23C and 23D are diagrams explaining the process of manufacturing the composite type magnetic head.
As shown in FIG. 22A, a plurality of composite type magnetic heads are formed on a semiconductor wafer 100 by a thin film technique. Next, as shown in FIG. 24B, the wafer 100 is cut into strips to make a plurality of row bars 101. A row bar 101 includes a plurality of the magnetic heads 102 arranged in one row. Resistance elements 102a are provided on the left and right ends, and at the center of the row bar 101 for monitoring the process of the manufacturing.
As described above, the height of the magnetic resistance film 83 for the magnetic head 102 is lapped to be constant or uniform. However, the row bar 101 is extremely thin, for example, about 0.3 mm. It is, therefore, difficult to mount the row bar 101 directly to a lapping jig, and as shown in FIG. 22C, the row bar 101 is bonded to a mounting tool or base 103 with heat dissoluble wax.
Then, as shown in FIG. 23A, the row bar 101, which is bonded to the mounting base 103, is placed on a lapping plate 104 for lapping the row bar 101. As known in Japanese Unexamined patent application published No. 2-124262 (U.S. Pat. No. 5,023,991) or Japanese Unexamined patent application published No. 5-123960, the resistance value of the resistance element 102a for monitoring is always measured while lapping the row bar 101. Then, it can be detected whether or not the magnetic resistance film of the magnetic head 102 has become a targeted height.
When it is detected by the measurement of the resistance value that the magnetic resistance film has been lapped to the targeted height, the lapping processing is stopped. After that, a slider can be formed on a bottom surface 101-1 of the row bar 101, as shown in FIG. 23B.
The row bar 101 is further cut into a plurality of magnetic heads 102, as the row bar 101 is mounted on the mounting base 103 as shown in FIG. 23C. Each magnetic head 102 is taken out from the mounting base 103 by heating and melting the heat dissoluble wax, as shown in FIG. 25D.
In this way, a row bar 101 including a plurality of the magnetic heads 102 is prepared, and lap processing is performed for the row bar 101. Therefore, the magnetic resistance film on the plurality of magnetic heads 102 can be lapped by one step.
FIG. 24 is an explanatory diagram of a conventional lapping apparatus.
The lapping apparatus has a rotary lapping plate 104, as shown in FIG. 24. A supporting block 105 has three pads 105a contacting to the lapping plate 104. The pads 105a smoothly spread slurry (abrasive liquid) on the lapping plate 104 and fill the slurry into the lapping plate 104. The pads 105a, further, may soften pressure of the supporting block 105 to the surface of the lapping plate 104.
The supporting block 105 is swung on the lapping plate 104 by a swing mechanism 106. The supporting block 105 supports the mounting base 103. Therefore, the row bar 101, which is bonded to the mounting base 103, is lapped by the rotation of the lapping plate 104 and the swing of the block 105.
In the conventional lapping apparatus, speed and pressure on lapping process are set as to be constant from starting to finishing the process.
It has been possible to reduce the time required for the processing by increasing rotating times of a lapping plate or giving higher pressure. Thereby, it becomes possible to save the time for the lapping process. However, there has been a problem to lower quality of lapping when the processing speed is increased.
On the other hand, when the speed for the lapping process is decreased to obtain good quality of lapping, there would be another problem to take much time for the lapping process.
It may be considered that a first lapping apparatus for speeding the processing up and a second lapping apparatus for speeding the processing down are employed together. After executing a coarse processing in the first lapping apparatus, a fine processing is performed by the second lapping apparatus. However, the work piece has to be set on the lapping apparatus twice according to the method, and therefore, troublesome for an operator and take much time. Therefore, it is unsuitable for mass production of the work pieces.